In the early days of the telephone art, use of the telephone was often confined to communications among users within a local geographic area. As a result and over the years, the economies related to accessing a communications system have lead to telephones in a local area usually being interconnected through a central controller, often called a local central office in the art.
As digital computers came upon the scene, another local community of use was discernible. Hence, a central controller is commonly employed for interconnecting various user terminals. For example, U.S. Pat. No. 3,851,104; entitled "Digital Communications System" and issued Nov. 26, 1974; discloses a time division, multiple access communications system which, under the control of a central terminal, provides communication links among a plurality of user terminals by way of a single communications signal path.
As the digital computer art advanced, parallel advances in the semiconductor art have lead to smaller, relatively inexpensive computers. With the advent of such smaller computers, the technique of central computer control is being abandoned in favor of a distributed control technique. Also, because of the usually bursty nature of digital information, the recent trend has also been toward communications systems having a capability for handling packets of digital information. One such distributed control communications system is disclosed in U.S. Pat. No. 4,063,220; entitled "Multipoint Data Communication System with Collision Detection" and issued Dec. 13, 1977. Indeed, the '220 patent discloses a communications system in which, when a terminal is to start an intended transmission on a communications path, a phased decoder detects the presence of other transmissions on the path and, responsive thereto, delays the intended transmission until no other transmissions are sensed. Once a transmission has started, if an interference (or collision) therewith is detected, a random number generator is used to select an interval of time at the completion of which the next transmission will take place.
Collisions being a problem, efforts exist in the art toward providing communication protocols for mitigating the deleterious effects of collisions. For example, one solution, called a slotted contention protocol, is disclosed in U.S. Pat. No. 4,161,786, entitled "Digital Bus Communications System" and issued July 17, 1979. Another solution, called an unslotted contention protocol, is disclosed in U.S. Pat. No. 4,210,780, entitled "Multiple Access Digital Communications System" and issued July 1, 1980. Unfortunately, the efficiency related to known multiple access digital communications system protocols tends to decrease as the digital signal bit rate increases, e.g., in a range of about 50-to-200 megabits per second.